[Python-Dev] package imports, sys.path and os.chdir()

Christian Tismer tismer at stackless.com
Thu Apr 26 23:30:40 CEST 2012


I have a small problem/observation with imports.

I have several packages to import, which works all fine, as long
as the packages are imported from directories found on the installed
site-packages, via .pth etc.

The only problem is the automatically prepended empty string in sys.path.
Depending from where I start my application, the values stored
in package.__file__ and package.__path__ are absolute or relative

So, if my pwd is the directory that contains my top-level modules,
even though sys.path contains correct absolute entries for that, in this
case the '' entry wins.

Assume this:

<- cwd is here

 >>> import moda

Some code happens to chdir away, and later some code does

 >>> from moda import modb

Since the __path__ entry is now a relative path, this second import fails.

Although it is no recommended practice to leave a changed chdir(), I
don't see why this is so. When a module is imported, would it not be
better to always make __file__ and __path__ absolute?

I see the module path, hidden by the '' entry not as a feature but
an undesired side-effect.

No big deal and easy to work around, I just would like to understand why.

cheers -- chris

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